This invention relates to an improvement of an electronic musical instrument of a type having tone sources which generate note frequency signals having shapes defining frequencies of the tone pitches of respective notes to be played by the keys on the keyboard.
A prior art electronic musical instrument having tone sources which generate note frequency signals having shapes defining frequencies of the tone pitches of respective notes to be played by the keys and selecting a required one or ones of such note frequency signals in response to depression of a key or keys must feed tone source signals of a number corresponding to a total number of keys on the keyboard (e.g. 61 tone source outputs if there are 61 keys) individually from these tone sources to a keyboard circuit. Accordingly, this type of instrument requires the same number of connection wires connecting the keyboard circuit and the tone sources as the number of the keys. This causes a problem in designing a portion of the instrument (except for the keyboard circuit) in an integrated circuit configuration since the integrated circuit requires a large number of connection pins (e.g. 61 if there are 61 keys) for connection with the keyboard circuit. Increase in the number of pins in the integrated circuit results in increase in the cost of manufacturing of the electronic musical instrument.
To eliminate the above described disadvantage in the prior art electronic musical instrument, the assignee of the present invention has proposed in U.S. patent application Ser. No. 671861 an electronic musical instrument capable of digitally processing signals in all circuits therein including a keyboard circuit and other circuits connected thereto for facilitating an integrated circuit design. In this proposed instrument, the tone source circuit includes twelve oscillators respectively generating note frequency signals having shapes respectively defining frequencies of twelves notes C through B of the highest octave and twelve sets of frequency dividing circuits each set of which divides in frequency the note frequency signal generated by a corresponding one of these oscillators sequentially for producing note frequency signals for a plurality of octaves for each of the notes C through B. This proposed circuit, however, is considerably complicated in construction and a further improvement has been desired.